Thermoplastics are compositions which can be molded or otherwise shaped and reprocessed at temperatures above their melting or softening point. Thermoplastic elastomers are materials which exhibit both thermoplastic and elastomeric properties, i.e., the materials process as thermoplastics but have physical properties like elastomers. Shaped articles may be formed from thermoplastic elastomers by extrusion, injection molding or compression molding without the time-consuming cure step required with conventional vulcanizates. Elimination of the time required to effect vulcanization provides significant manufacturing advantages. Further, thermoplastic elastomers can be reprocessed without the need for reclaiming and, in addition, many thermoplastics can be thermally welded.
Block copolymers containing alternating "hard" and "soft" segments within the copolymer chain comprise one well known class of thermoplastic elastomers. Other classes of thermoplastic elastomers derived from inexpensive and readily available raw materials comprise thermoplastic blends of partially cured monoolefin copolymer rubber and polyolefin resin and dynamically partially cured blends of monoolefin copolymer rubber and polyolefin resin, W.K. Fischer, U.S. Pat. Nos. 3,758,643 and 3,806,558. Products are obtained which process as thermoplastics provided that conditions are controlled so as to obtain only a partial cure. Although the partial cure may increase the strength of the product, the tensile strengths are still so low as to limit potential applications for these materials. The present invention provides vulcanizates having greatly increased strength but which are nevertheless thermoplastic.